text:
Is the FAA the only authority with specific medical requirements for transgender pilots?
The FAA/CAMI imposes certain testing requirements on transgender pilots, listed in the Guide for Aviation Medical Examiners under Item 41 (G-U System), subheading "Gender Identity Disorder".
Is the FAA the only authority that has these requirements, or do other countries have similar policies?
EDIT:
the link above is broken but I think there might be value leaving the old URL in case people want to try to get there on archive.  The updated reg is at https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item48/amd/gd/

Also, transgender persons are not as widely accepted in many countries as they are in the USA.  I wouldn't be surprised if most countries didn't even consider this.

Does anybody know if ICAO regulation covers this at all? Because if so, we can get a pretty easy global answer. Otherwise, it will be country by country - all 191 member states (except for situations like the EASA)

@raptortech97 my inability to find anything regarding this from the ICAO is why I finally came here and asked.  It exceeded my search pain threshold.

@kjmccarx And in the USA, being transgender means you get described as having a "disorder", made to undergo psychiatric testing and assumed to be abusing/misusing substances. If only every country were so accepting!

The European Association of Social Anthropologists makes searching for European answers surprisingly difficult! Oh, and for anyone who wants to read an incredibly offensive article of how the FAA was dealing with this in 2009 see page 6 of this article: http://www.faa.gov/other_visit/aviation_industry/designees_delegations/designee_types/ame/fasmb/media/200904_color.pdf

@DavidRicherby at the danger of getting off-topic, the American Psychiatric Association has repeatedly stated that being trans is not, in itself, a disorder, e.g. here:  http://www.psychiatry.org/File%20Library/Learn/Archives/Position-2012-Transgender-Gender-Variant-Discrimination.pdf.  My nascent attempts to inform the FAA of this prompted me to ask this question.  I'd be happy to talk more about what I'm doing in chat at some point.

I got half way through that article, @raptortech97. The constant misgendering was getting to me. You weren't wrong about its being offensive.

@TRiG yeah, that's about half of why I don't plan on getting a PPL.

FYI commenters, the FAA medical regs have changed as of TODAY.  See https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item48/amd/gd/
Still not great, but better.

As several commenters have noted, medical rules are different in each country. ICAO provides guidelines and recommendations, but it's up to each country to actually implement them. ICAO's personnel licensing requirements are in Annex 1 which is not freely available but their Manual of Civil Aviation Medicine implies that transgender pilots should be considered 'higher risk':

Applicants with disorders of behaviour (for example regarding habit,
  gender identity, sexuality) should be assessed on the basis of their
  ability to put aside the disorder (or any conflicts related to the
  disorder) in order to attend to the aviation task at hand. These
  persons may have significant conflicts with their environment, leading
  to further difficulties, which may become an impediment for them to
  hold an aviation licence.

Looking at specific countries, the FAA may be an unusual case by explicitly mentioning gender identity issues. I couldn't find any mention of them in the EASA, Canadian or UK medical requirements. But all countries' medical requirements include something general like this (this example is from EASA):

(g) Personality or behavioural disorder Where there is suspicion or
  established evidence that an applicant has a personality or
  behavioural disorder, the applicant should be referred for psychiatric
  opinion and advice.

That catch-all clause would - I assume - include gender identity disorder and therefore require psychiatric evaluation of the pilot. And in cases where a pilot has had gender reassignment surgery and/or drug treatment, the surgery and drugs regimen would almost certainly trigger additional testing and investigation (so would any other major surgical procedure or long-term drug treatment).
Finally, it's worth noting that whatever the general rules are, every case is different and the only way to get a specific answer for an individual is to consult with an aviation medical examiner for that jurisdiction.
(Disclaimer: I know nothing about medicine except that it's complicated. Consult an aviation medical specialist if you want a real answer.)

This answer is tremendously useful and is precisely the sort of thing I'd been after.  Sources and quotes!  Thank you.

@ErinAnne That is exactly what this site is intended for, glad we could help!  If this answers your question, you can accept the answer by selecting the check mark near the top of his answer.


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What is the Hot Air Pressure Regulating valve and what's its purpose?
What does the hot air pressure regulating valve do, yes I know that it regulates hot air pressure but what does that do, create hot air? How does it regulate hot air pressure?
I have a picture of the valve here at page 3. It's an Airbus A320
http://www.smartcockpit.com/docs/A320-Air_Conditioning_and_Pressurization.pdf

The valve regulates the pressure of hot air from the engine bleed system that bypasses the airconditioning packs. This hot air is then fed to the trim air valves to adjust cabin temperature.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
Could the wing struts on the SUGARVolt cause problems?
On Boeing's concept aircraft, the SUGARVolt, there are wing struts connecting the fuselage and the wings, which is for making sure that the wings do not bend too much during flight.

Could the wing struts cause aerodynamic instabilities, and could this make the aircraft more efficient, or less efficient? In what ways?

Struts like those on the SUGAR Volt and SUGAR Freeze have been used on gliders and propeller aircraft without problems. Since they are loaded in tension, they can oscillate like the string on a guitar. Note that they are braced at two thirds of their span to reduce their free length and to increase their resonance frequencies. A coupling between the strut bending motion and oscillating aerodynamic forces can be expected, but only at speeds above the SUGAR Volt and SUGAR Freeze design speed.

Henschel 126 with a very similar strut arrangement. Only with the strut it was possible to reduce the wing chord at the root in order to give the pilot better upward visibility (picture source).
Those struts do indeed reduce drag. They cause friction drag but allow to build the wing much lighter, thus reducing the required lift and the inevitable induced drag.
Modern gliders have very similar wings but do not use struts. This might seem puzzling, but can be explained by the low payload of a glider, which is at most two humans and their equipment. In order to fly faster, gliders use water ballast to make their wings even heavier. Therefore, a glider will not benefit from a lighter wing.

Nimeta single-seat glider (picture source)
In contrast, a revenue-generating aircraft needs to pack as much payload as possible. It cannot afford to carry unnecessary weight around in its structure. Also, a lot of its mass is concentrated in the fuselage, which increases the wing's root bending moment. A strut will help to reduce the root bending moment greatly and will enable a much lighter wing structure.

In this video it looks like the struts won't make any lift. According to Boeing the airplane is designed to make more lift than planes today so it's totally more efficient.
The struts make the plane less efficient in theory, but without them the wings must be much shorter and then it's even less efficient.

Struts on such an aircraft would almost certainly be airfoil-shaped to reduce drag, not "just straight". Then their lift/buoyancy would depend on the angle of attack. Camber would have some influence but it is not absolutely necessary; there are airplanes whose wings have no camber.

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text:
Are the IMU velocities equivalent to the GPS ground velocity, except for the coordinate reference system?
If the velocities measured by the IMU in the body-fixed reference frame are converted into earth fixed frame, are they equivalent to the ground velocity measured using the GPS?

You question is a good one but its writing makes it hard to follow. You should edit it to highlight why you think it may or may not be the same speed and what distrubs you enough to post this question. That way, the answer will be more specific and complete.

An IMU uses gyro and accelerometer measurements to calculate its velocity vector relative to the Earth.   Similarly, a GPS uses range, range-rate, doppler, and/or carrier phase shift measurements to several satellites to calculate the same velocity vector.  So, an IMU and a GPS calculate the same velocity vector, but use different measurements.
The difference between the IMU and GPS measurements are that, inherently, an IMU has very good short-term accuracy but drifts over longer periods of time;  a GPS has very good long-term accuracy, but is very noisy over short periods of time. Therefore, IMU and GPS measurements are usually combined to provide a navigation solution that is accurate over both the short-term and the long-term.
The components of the velocity vector are usually given in a local-level, local-north reference frame; for example, the north- east, and down components: $v_N$, $v_E$, $v_D$. The ground speed is $v_H=\sqrt{v^2_N+v^2_E}$.

You are correct @mins. I will edit my answer, but still keep its simple.


text:
What trade-offs does an airline make when selecting an engine type for their aircraft?
So it is my understanding that on most commercial jets, the airline has a choice of multiple engine types, such as GE or P&W, etc. My question would be why an airline would choose one type over the other. Also if there is a "better" choice, why would the airlines choose one of the others?

good question - was wondering the same after a recent question on engine costs seemed to suggest large differences on list prices (limited data).

Similar question: What are the advantages of the Airbus New Engine Option (NEO) program?

Seems like obvious considerations would include: maximum thrust (and its effect on maximum payload), fuel burn, weight, price, reliability, maintenance costs, financing options, ... With all these trade-offs, there's no particular reason why one engine should be objectively "better" than another.

I have no idea, but I would guess the primary consideration is existing maintenance capabilities for one or the other.

Power
Some models are different in power, a consideration if you intend to operate hot and/or high, or heavy. Otherwise that extra power is mostly fuel-inefficient.
Competition
In situations where two or more alternatives are available, there's healthy competition. Engines are around 25% of the cost of a new aircraft, so there would be a big money to gain when airlines bulk order from a certain company.
Boeing took this a step further on the B787 where it's easier than ever to switch the type of engine to prevent this type of 'vendor lock-in'. Historically,  it was very difficult to switch due to the technical complexity in these systems.
Customer Relationship
If an airline has good contacts with a manufacturer and know how they work, they may prefer to opt for that comfort when considerable money is on the line.
Part Commonality
The more type of the same engine you operate, the better economies of scale you achieve. This is especially important as substantial maintenance work is concentrated around the engines.
This made for instance American Airlines store Boeing 757 aircraft that it got through a company acquisition that did not have the same engine type as the remaining fleet.

This thinking is not limited to your company, but for instance within a group of companies, as heavy maintenance is often centralized.
It can even apply across types. For instance, Korean Air ordered 787s and 747-8 both with GEnx engines. To quote GE Aviation on the two slightly different engine types:

The -2B contains an identical core and similar materials as the -1B, delivering synergies for mixed GEnx fleets

Thanks for the detailed answer! Looks like it is an airline specific business decision more than anything.

Part commonality sometimes work in the opposite way, when you don't want your company to be at mercy of one manufacturer.


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While only RL will be sufficient at night for the aircraft to take off, both RL and RCLM are required to take off during the day. Isn't it illogical?
While only Runway Lights (RL) will be sufficient at night for the aircraft to take off, both RL and Runway Centre Line Markings (RCLM) are required to take off during the day. Isn't it illogical? The image is taken from the low visibility take-off section of the 10-9 page Jeppesen chart of Tekirdağ Çorlu Airport (LTBU).

For those of us unfamiliar with the acronyms, the question is referring to Runway Lights and Runway Centre Line Markers.

To me it makes perfect sense if you consider that at night there is high contrast between darkness and the lights. It is easy to make out the runway edge lights through the fog under darkness, so the lateral position of the aircraft on the runway and its alignment with the runway can be estimated from lights only.
Under daylight conditions the fog itself is scattering the sunlight. The contrast between the runway lights and the scatter is much lower, preventing the pilots seeing lights further down the runway. Therefore during daylight, the runway's center line markers are required so that pilots can see the lateral position and alignment with the runway.

 Image sources: Day landing and night landing
These images show how much more pronounced the edge lights are at night compared to during daytime.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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What is the thrust specific fuel consumption of a JT9D engine used for the Boeing 747SP?
I searched every inch of the internet still couldn't find the value of JT9D thrust specific fuel consumption (TSFC) , I just found the SFC which is around 0.37.
Can anyone help please?

Hi saad, welcome to aviation.stackexchange. I am made a few modifications to your question, I hope you don't mind. You can always edit your question to improve it further.

You could help the community in answering your question by adding a bit of information: for what phase of flight are you looking for the TSFC? Where did you find the SFC ( a link would help) and what units is the SFC in?

The answer is not available online. You probably have to look for it in the McGraw-Hill Aviation Almanac or one of Jane's books, which are not available on the web. The reason why its hard to find is that there is not one number for that question. It varies on the basis of many different factors.

I somewhat doubt the “SFC” you have is really power-specific rather than thrust-specific, because as far as I can tell nobody ever quotes power for turbojets and turbofans. But you really need at least two values, because for a turbofan the TSFC at cruise speed is usually around twice as much as the static one (but (P)SFC wouldn't be any better, the performance characteristics is such that both change significantly with speed).

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Does a non-current private pilot need to renew his license to obtain a Part 107 (Remote Pilot) certification?
I am a non current private pilot (haven't flown for about 15 years) that need a 107 license for work to fly DJI drones.
my employer is not going to pay around $1,000 to get me current again (it's been a while. I will need some ground school and some practice to get to my groove).
Can I just take the 107 course and only get the remote pilot? or since I'm a pilot now, I need to make my private pilot current as well?

I would suggest contacting the FAA at https://www.faa.gov/uas/contact_us. They can provide the proper guidance.

See 14 CFR 107.61(d).
If you do not meet the flight review requirement of 61.56, then you do not qualify to get a Remote Pilot License by taking the training described in 107.73.
However, you can still get one by passing the knowledge test described in 107.74, same as a non-pilot.


text:
What is the holding speed for a CAT B aircraft?
What is the airspeed for holding area construction for a CAT B aircraft in a hold under normal conditions at 4,250 metres (14,000 ft)?

What country are you flying in?


text:
How to determine unique fix and navaid identifiers in FAA data?
I want to import data the data in the .csv file in the FAA NASR Data data but am finding that some navaids and airports have the same names.  Does anybody know if fixes are unique in regards to airports and navaids?

look at the "NAV DATA LAYOUT" Word doc that's in the NASR zip file. Each of the different NAV csv files will have an "ordered by" specified. The unique identifier is actually like a compound key, not a single field. For the NAV_BASE file it's NAV_ID + NAV_TYPE + COUNTRY_CODE + CITY. That's how much it takes to make each unique.

That looks like that will make them unique.  Aren't they all in the US though?

There are some in Canada, Mexico, and the Caribbean. I guess they're close enough to be used when flying in the US as well as the owning country, so that's why they get included.

Your language is not, strictly speaking, accurate, which may be causing some confusion.
Let us take an example: the airports and NAVAIDs near Omaha, Nebraska.
There is a civil-use airport near Omaha, NE, with the following characteristics:

Name: Omaha/Eppley Airfield
FAA Location Identifier: OMA
IATA Identifier: OMA
ICAO Identifier: KOMA

There is a military-use airport:

Name: Offut Air Force Base
FAA Location Identifier: OFF
IATA Identifier: OFF
ICAO Identifier: KOFF

There is a NAVAID:

NAME: Omaha VORTAC
Identifier: OVR

There is another NAVAID:

Name: Offut TACAN
Identifier: OFF

Offut TACAN is located on the property of Offut Air Force Base, but as Michael Hall alluded to, the two locations do not share the same geographic coordinates.
There are many examples where a NAVAID's identifier is the same as an airport's FAA LID—for most of those examples the names are also the same (as at Offut) but some where they are not (IAH, "Houston/George Bush Intercontinental Airport," and IAH, "Humble VORTAC"). Then there are examples where the names are the same but the identifiers are different: LEX, "Lexington/Blue Grass Airport," and HYK, "Lexington VOR-DME."
Fixes and waypoints do not have "names" as such. Their five-letter identifiers are designed to be pronounceable on their own (some imagination required). Therefore there should be no conflict between a fix/waypoint and a NAVAID, even when waypoints have been designated with the intent of replacing a NAVAID (LWM, "Lawrence DME," and LWRNC waypoint).

+1 for (some imagination required)! Within a facility, is there a set standard of "how we pronounce this fix," or is it left to controllers' imagination, as it is for pilots? For example, LITME (near DC)... is it "lit me" or "lie t' me"? Is the Dallas arrival the "Jeffrey" or the "J-Fry"? Leaving LA, is CNERY "scenery" or "Connery"? Inquiring minds...

I've seen a PDF of an "official pilot's guide" put out by one specific facility (I want to say it was CLE?) but besides that it's just institutional knowledge that gets passed down during on-the-job training. And the pronunciation that was intended by the procedure/airspace design team may not always stick in the operational environment.

Yes, they are unique.
No two airports or navaids with the same name share the same Latitude and Longitude.  (That might sound snarky, but that isn't the intent!)
The reality is simply that you eventually run out of pronounceable names and may have to reuse some.  Location is how they are differentiated.
Did I interpret the question properly?

I am actually importing into a database and so far I do not see any fixes with the same names as airports or navaids.  I need to have a unique identifier and cannot use name and lat/long.  There are lots of airport that have the same names as navaids but I am going to use the ICAO name for airports that conflict.

In the US there are plenty of Navaids with the same 3 letter identifier as an airport.  Not all are co-located either, which is why it's important to make sure you differentiate by adding the "K" if you want the airport.  Is that what you are getting at?


text:
Can I get an EASA class 2 medical certificate, if my myopia is corrected by glasses?
Yes, I know somebody asked this question before but I am still confused

(2) For a class 2 medical certificate:
(i) Distant visual acuity, with or without correction, shall be 6/12
(0,5) or better in each eye separately and visual acuity with both
eyes shall be 6/9 (0,7) or better.
(ii) Notwithstanding point (b)(2)(i), applicants with substandard
vision in one eye or monocularity may be assessed as fit, in
consultation with the medical assessor of the licensing authority and
subject to a satisfactory ophthalmological evaluation.

Its says "with or without correction"; if the regulation is like that, it is possible for everybody to get a class 2 certificate. Because there is no limit for myopia.
I have myopia -6 (L) -5,50 (R), does this mean that I can get a class 2 certificate with glasses?

You are confusing visual acuity of the eyes in general with the optical power of the lenses required to correct your myopia.
Depending on where you are from, you may be more familiar with the visual acuity, or visus, expressed in 20/x (United States) or a percentage/decimal value (e.g. 80 %, 0.80) (e.g. Germany). The decimal value for acuity is also stated in parentheses in the regulation (6/12 == 0.5, 6/9 == 0.7).
Since visual acuity depends on several factors, the myopia may or may not be bad enough for you to not get a Class 2 medical. If you only achieve sufficient acuity with glasses, then the medical will require you to wear suitable glasses or contact lenses when acting as a pilot.

As always, it's a good idea to have a consult visit with your AME with any concerns you have with your medical history BEFORE your medical exam. Your AME will be able to let you know what the cutoffs are for any conditions you're worried about.


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What drives the design decision of where to place the refueling receptacle?
What has driven the decision to place the refueling receptacle behind the pilot and to rear of the plane.  Is this simply driven by the change away from drogue and probe and the location decided by the preference of the pilots, the manufacturers or the service, any ideas?
As earlier aircraft appear to of a variety of locations of the receptacle.
I realize the pilot does not have to fly the probe into its receptacle, that is done by the tanker operator.

It seems the preffered location (safety-wise) is behind the cockpit, ie the F-16 and the F-35 (only on the A model. the B model has the VTOL fan in that location and is using drogue and probe anyway. C is also using drogue and probe) Except that: On the F-15 you have the airbrake, and then you'd get too close to the tail fins. Same holds for the A-10 (too close to the engines/tail fins). On the B-1B there is the weapon bay ( I guess you wouldn't want fuel flowing around that...)

B2 Also has it further rear also, F-22 also, the only reason to move it further back on the aircraft is to move the probe away from locations that damage is less consequential.  As in not screwing with the stealth capabilities, sensors and aerodynamic performance.

Side note: Dassault fighter jets (Mirage 2000, Rafale) have them in front of cockpit.

Also: OP statement that the probe is driven by the operator is not always true. Again, French airplanes need the pilot to fly the plane "into" the cone.

@kebs: The OP was referring to the boom of flying-boom systems, not the probe of probe'n'drogue systems (yes, I know it was a poor choice of words on their part).

Usually just a matter of constraints on where the engineer can physically fit the fueling port with the limits that it must be an upper surface, not too near critical components that may be damaged, and have minimal aerodynamic impact. The plane must also deal with the substantial change in center of mass and angle of attack[required lift] during the fueling. All these factors vary with the design goals of each model.
The drogue and probe method is used by the US navy and most international air forces. This is a very adaptable system that can fuel multiple small planes from wing mounted hoses on one tanker or small plane to small plane, and even works with helicopters(using a very long probe); the down side is that maneuvering to couple is more difficult and each drogue design has a narrow speed range. The probe must be in located view of the pilot.
The port and flying boom method is used by the United States air force; it was developed by the strategic air command early in the cold war for strategic bombers. As such the flow rate of the flying boom is an order of magnitude larger than the hose and probe, and it can be used across a very wide speed range without changing parts, with added benefit of no probe to effect drag, radar signal, or to get damaged; the downside is the tanker can only serve one plane at a time, the port must be on an upper surface, and the tanker needs a boom operator.


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How can LMT be converted to UTC time?
I am trying to solve some problems on converting from LMT (local mean time) to UTC (coordinated universal time) for flight planning purposes and I have some doubts. The problem is the following:
If the LMT in Delhi (LON=85ºE) is 17:45 (5:45 PM), what is the UTC?
First of all, what I've done is converting longitude into time as follows:
$$t=85\cdot4=340\hspace{1mm} min=5h\hspace{1mm}40m$$
But then, in order to compute the UTC time, what do I have to do, either adding up this time to the current LMT or subtract it (and what is the reason)?
$$UTC=Delhi(LMT)\pm t$$
I have checked a website that allows you to convert from LMT to UTC (https://savvytime.com/converter/lmt-to-utc-india-delhi) and I've seen the solution is 11:15 PM.
However, if I add or subtract my result, it is not the same as the given in the website. I suspect it is because in India they are using UTC +5:30 and probably these equations do not contemplate that, but I want to know the opinion of the experts anyway.

UTC time is used by pilots and flight planners to calculate the ETA at the destination airport. This exercise is obtained from an Pilot's Handbook, and in my opinion the question is suitable for this forum, provided that there is no other in which it may fit better (a tag called "time" exists and its description says that is for UTC related question). Furthermore, a lot of people involved in this forum (pilots, aerospace engineers, et cetera) are familiar with this topic and might be able to help. @mins

I guess in that case this is not local mean time (which follows the sun and varies each day, up to 30 minutes over the year) but local time (civil time) based on UTC and time zones.

Local Mean Time is not currently in common use in aviation. India Standard Time may have been originally based on the solar local mean time relative to GMT but for the purposes of answering your original question you should use IST, or UTC + 5:30.

@mins Are you not confusing local mean time and solar time?

@Airman01 When converting longitude to time, why do you multiply it with 4?

@mins: I just copied the statement of the problem as it is in the book. I think I'm not confusing it because of the answer below. But I know it's confusing because of the Wikipedia article you showed.

@Farhan yes, it is due to Earth rotation that we can establish a relationship between longitude and time. If 15 degrees are one hour, 1 degree is 4 minutes.

@JonathanWalters: After checking again, I see it's me that was confusing solar mean time (used for the civil time) and solar (apparent) time (indicated by the sundial) and didn't get well the definition at first. The two differing by the equation of time of the day at the location. I apologize for suggesting Airman01 was wrong. Thanks for pointing this.

Why is this question getting downvotes? Do users not understand that this is an aviation subject?

You have almost solved the problem yourself. The website you linked to does not help you because, for some reason, it assumes Local Mean Time (LMT) to be equal to UTC. For your problem, LMT needs to be for 85° of East longitude. So, ignore that website and let's move on.
For every degree of longitude, you calculate 4 minutes of difference from UTC. You have already correctly calculated the LMT difference from UTC for 85°E:

First of all, what I've done is converting longitude into time as
  follows: $$t=85\cdot4=340\hspace{1mm} min=5h\hspace{1mm}40m$$

This leaves you with the question of whether to add or subtract this difference, as you stated:

But then, in order to compute the UTC time, what do I have to do, either adding up this time to the current LMT or subtract it (and what is the reason)?

Let me start with the reason—the explanation of why we want to either add or subtract the difference between LMT and UTC—and then give you the solution.
LMT can be thought of as roughly equivalent to time based on the Sun's position. It is not equivalent to that, which is Solar Time, but it is related. Keeping that approximation in mind, consider the difference in time between when the sun reaches solar noon over Delhi, and when the sun reaches solar noon over London. As the earth rotates, the sun reaches solar noon first over Delhi, and then, a few hours later, over London. Thus you know that UTC will be a few hours behind Delhi LMT. This means that you need to subtract the calculated difference between LMT and UTC.
Another way to put this is: LMT for East longitude is ahead of UTC (subtract the difference to find UTC), and LMT for West longitude is behind UTC (add the difference to find UTC). Thus a more proper way to perform your calculation mathematically would be to properly incorporate the negative sign:
$$t=-85\cdot4=-340\hspace{1mm} min=-5h\hspace{1mm}40m$$
Therefore, if the LMT in Delhi (LON=85°E) is 17:45, then:
$$UTC=12h05m$$

Perfect! Now I understand everything, I was very confused because of the website but now I see I was not so much lost. So when I said LMT (local mean time) is that correct? Because @mins said I was confusing "local mean time" with "local time", I just copied the statement of the problem right as from the book. Thank you so much for the answer.

@Airman01: This is correct, I made a mistake reading the definitions. LMT = civil time. Jonathan has a clear explanation on that. An article about time in maritime navigation that also talks about the difference.

Actually, that is NOT correct.  LMT is related to the solar position at a longitude, and is what the answer here gives.  Local time is based on politics and includes thing like daylight saving time, etc.  One cannot figure out local time from a formula alone.  You must know the offset from UTC (including any DST rules) in effect for the date and time being converted.  This is decided by governments, not by math.  Computers use the tz database for this.

@MattJohnson I fail to understand what you are referring to as "NOT correct". The information you offer above seems to affirm both my answer as well as the other comments on this question. What do you intend to address by your comment here?

The part in the second comment here (by @mins) that says "LMT = civil time".  Civil time is local time, as used by people on the ground, which is controlled by governments.  LMT is the longitudinal time that you correctly describe in your answer.

@MattJohnson OK, now I understand. Do note that "civil time" has at least two definitions, of which the traditional one is related to mean solar time and can be derived by formula. Also note that to address a comment by a specific user you may include their username, like this: @mins.

Use this simple Formula:-
For places with East Longitude
LMT = UTC + dLong/15
For Places with West Longitude
LMT = UTC - dLong/15
(Where dLong = Distance between the two Longitudes)


text:
Is there a rule concerning the offloading of a missing passenger's baggage?
Is there an International Rule under which the baggage of a passenger is offloaded in the case that he/she fails to report at the departure gate 15 minutes before boarding time?

VTR.  The OP posted this question as an answer on the question marked as duplicate.  The deletion comment requests that they ask a separate question as they have done here, only for it to be closed as a duplicate.  The answers to that question do not answer the question posed here which is specifically asking about regulations.

Possible duplicate of Is baggage always offloaded when a passenger does not travel?

This question was covered over on travel.stackexchange and seems like there is a European reg on it.

In Europe, the question is covered by Regulation EC 300/2008. Annex I,
  section 5.3 reads
Baggage reconciliation

Each item of hold baggage shall be identified as accompanied or
    unaccompanied. Unaccompanied hold baggage shall not be transported,
    unless that baggage has been either separated due to factors beyond
    the passenger’s control or subjected to appropriate security controls.

I cant find any hard regulations but there seems to be some discussions floating around that would imply a domestic US flight may depart with your bags and without you here in the states.
I can speak from experience while on a flight departing CDG for DUB the plane was held to remove a bag that belonged to a passenger that decided to take a different flight.


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What are the criteria for classifying which generation a fighter aircraft belongs to?
Current jet fighters have been classified as 4th generation, 4++ generation, and so on, with 5th generation being the latest, i.e F- 22. What is the criteria for such segregation? B-2 is a stealth aircraft but considered 4th generation whereas Mig-35 is classified as 4++.

How can the B-2 be classified as a 4th generation fighter?

B-2 was a bomber aircraft so might be wrong example here, its counterpart F-117 Nighthawk was 4th Gen.

F117 isn't really a fighter, either.

In terms of stealth, the F117 is really 5th gen, if you subscribe to these marketing terms.

The Wikipedia Page for Fighter Generations has a relatively comprehensive list on how they derive at the "generation" of the fighter. For example, here is how the Air Force classifies them:

1: Jet propulsion : F-80, Me 262
2: Swept wings; range radar; infrared missiles : F-86, MiG-15
3: Supersonic, pulse radar, Beyond-visual-range missiles : Century Series, F-105, F-4, MiG-17, MiG-21
4: Pulse-doppler radar; high maneuverability; look-down/shoot-down missiles : F-15, F-16, Mirage 2000, MiG-29.
4+: High agility; sensor fusion; reduced radar signature : Eurofighter Typhoon, Su-30, F/A-18E/F, Rafale
4++: Active electronically scanned arrays; continued reduced signatures or “active” (waveform canceling) stealth technology, supercruise : Su-35, F-15SE
5: All-aspect stealth with internal weapons bays, extreme agility, full-sensor fusion, integrated avionics, some or full supercruise : F-22, F-35,
6: extreme stealth, morphing capability, smart skins, highly networked, extremely sensitive sensors, optionally manned, directed energy weapons.

Until we have a major leap in technology, it would seem we are capped off at 5th generation fighters for the moment.

Regarding 6th gen, what exactly is "morphing" defined as?

I'm not sure, but I think it may be somewhere in science fiction fantasy.

@Ksery: Changing the shape of the aircraft. Think a bird's wing, not Transformers.

Frontiers are blur. 4th and 5th generation get frequent upgrades that make them have features from 5th and 6th generation (sensor fusion, (active) stealth, networked, better and better avionics and sensors). And also what's the difference between "high agility" and "extreme agility"? is there a list of aerobatic maneuver that cannot be done if you are only "highly agile"?

There is no criteria because there is no such thing as an X-Generation fighter.  That Fourth Generation / Fifth Generation stuff is a marketing gimmick cooked up and used by aerospace OEMs to sell hardware at defense trade shows.  Nobody in the real world subscribes to this or even considers such nonsense.  There are either fighters or there are targets.  Nothing more, nothing less.


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Could airliners' wings be thinner if no fuel were stored in them?
I ask this question because wings are pretty thin overall, but I am curious if you could make them more thin.

Making them more thin at the Reynolds number they operate in may actually increase their drag. I can't remember the name of the guy but around the time of WW1 a German aerodynamicist discovered that thick airfoils had less drag on planes big enough to carry people (thinner airfoils are more efficient on drones and model airplanes). That is why all WW2 and modern planes have thick airfoils compared to the very thin airfoils of WW1 planes.

@slebetman Junkers?

@cpast: No, I think it's Prandtl at Gottingen University. The series of airfoils produced bears the designation "Gottingen". Though, Gottingen series airfoils continues to be produced by the university later under various other professors.

Hmm.. googling around led me to the fact that the person who first proposed thick airfoil was Nikolay Zhukovsky (Joukowski). Perhaps Prandtl was the first to test it out in a full-size wind tunnel.

@slebetman: That is the reason that the fuel is in the wings! It is pretty much the only thing that could effectively use up that space. Also, on some aircraft I believe that the fuel actually acts as a heat sink for the wing.

@cpast: Ludwig Prandtl, working at Göttingen University. (The diaeresis is non-optional I am afraid. ;-) ) He did all kinds of airflow research.

No.
The wing thickness is primarily dictated by structural demands. It has to provide an aerodynamic fairing for the wing spar. Making it thinner would drive up the mass of the structure inside.
To simplify things, imagine the wing spar as an I-beam. It has two flanges which carry tension and compression loads, and a web between the flanges to transmit shear loads. The bending moment carried by the spar is the product of the forces in the flanges and the distance between them. If you reduce the distance, the forces need to increase to keep the bending moment constant. Bigger forces will result in bigger flanges to keep the stresses in the material below the yield stress.
Limiting the thickness is the desire to fly at a certain Mach number. A moving wing needs to push the air ahead of it aside, and thicker wings need to do more pushing. This results in a higher acceleration of the flow around the wing, and thicker wings have a lower critical Mach number (the flight Mach number when local flow reaches Mach 1). This drag penalty is especially severe in supersonic flight.
Thicker wings also help with creating higher maximum lift coefficients, up to a point. The plot below (taken from this website) shows that an airfoil thickness of 12% gives the best results, which helps to keep the wing area low. A thicker wing also makes it easier to integrate complex high-lift devices, which again helps to reduce wing area.

The resulting wing thickness is always a compromise, and the fuel volume is only the result of that compromise. If a wing needs to store more fuel, the designers will choose a lower aspect ratio, but will leave the relative thickness unchanged. If less fuel is required, the tanks will become smaller, and again the thickness will not change.

Airplane wings are designed purely from aerodynamic and structural considerations. Supersonic fighters often have much thinner wings (and store fuel in the fuselage) because those are the requirements of supersonic flight. For subsonic (and transonic, which most modern airliners and business jets are -- over some parts of the wing the airflow is actually supersonic) flight, thick wings are fine, are structurally much better, and provide space for fuel tanks and the wheels.

I'm somewhat suspicious - Concorde was definitely supersonic, by a significant margin (Mach 2+) and yet stored fuel in the wings.

I agree, and I think the main reason fighters do not carry fuel in their wings is to reduce the danger from the opponent's weapons.
Furthermore, I can image they want to keep the weight as close as possible to the centerline to improve maneuverability.

@ROIMaison: Many fighters do carry fuel (also) in their wings. Probably most of them, even.

@Jan Hudec, You're right, I did some searching, and found this thread, saying that around 20-30% of the fuel is in the wings
http://www.airliners.net/aviation-forums/military/read.main/147729/ , it has a good example, but no good sources on general trends :(

@MSalters: The WP article on the F-104 has something to say about that: Lockheed found that small, thin trapezoid wings are best for high-speed flight. But that means, no wing-mounted landing gear or engines, and a very high landing speed. It's easy to see how this would be a problem for a plane the size of the Concorde -- structurally (landing gear), acoustically (engines), and safety-wise (landing speed).

@MSalters: thinness is a ratio. The root chord (distance from leading edge to trailing edge) of Concorde is around 100 feet; supersonic fighters are much smaller and have a much smaller volume in the wings -- especially when you take into account the structural members that have to share that space.

Possibly, but having no fuel in the wing would likely be an effect of making wings thinner, rather than a driving cause.
In the past, thin airfoil theory ruled the day, and designers used external trusses to support two lifting surfaces in a biplane configuration.  Check out the De Havilland Dragon, which used the RAF 15 airfoil section (max t/c of 6.5%), as an example.  Compare this to the Boeing 247, which was introduced one month later (May vs. April 1933) and also carried ten passengers, but used a single cantilever wing, without external supports.  Its wing section, the Boeing 106 (max t/c of 13.5%), was thick enough to contain an internal support structure.
The main benefit of having all your structural members contained in the wing is the reduced drag.  You get some other benefits as well, like delayed stall due to the rounded leading edge, and room to store your fuel due to the higher enclosed volume.  It's unlikely that any serious airliner design is going to return to a biplane configuration.
Today, thanks to the wealth of materials and design tools the engineers have, the wing thickness seems to be around 10% based on glancing at a few Airbus/Boeing offerings.  Usually, a modern design will change the airfoil profile from root to tip, so it will be higher in some places and lower in others.  It's possible that if these techniques were applied to biplane designs, we could come up with some really thin wings, but the airplane would have high drag and likely wouldn't sell.
That said, some concepts arrange the wings in ways that might let you get away with this.  In particular, Lockheed Martin has proposed a box-wing concept (for which I couldn't find the name) and Boeing has studied a design with braced wings called Subsonic Ultra Green Aircraft Research (SUGAR).  If one of these designs ends up reducing the amount of stiffness needed in the wing spar, the designers would likely reduce the spar (and thus wing) thickness to save weight.  Depending on how much thickness they shave off, it might no longer be worthwhile to store fuel in the wing.


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Does the rate of turn increase or decrease by turning at a higher speed?
It is easy to derive a formula for rate of turn in a steady banked turn as:
$$\dot\psi=\frac{g \cdot tan\phi}{v}$$
which indicates that as speed increases rate of turn decreases. This feels counteruntuitive especially given the identity for circular motion:
$$\omega=\frac{v}{r}$$
which would suggest rate of turn increases linearly as speed increases.
Can someone give me some intuition as to why speed has the opposite effect in a banked turn. Given the above I can only think that speed in a banked turn increases radius at a rate greater than it should increase $\omega$ during normal circular motion.

For an "intuitive" explanation, see the top answer here: https://aviation.stackexchange.com/questions/26467/what-is-the-relation-between-airspeed-and-rate-of-turn/26469#26469

The first formula is a function of bank angle $\phi$ and the velocity $v$. By varying only $v$, you are keeping $\phi$ constant. As a consequence, to keep the turn "steady" and coordinated (that are the assumptions needed to write that formula) you need to increase the radius of turn $r$ and decrease the turn rate.
The second formula is a function of $r$ and $v$. Once again you change only $v$, $r$ will be constant here (while before was $\phi$). This leads to a turn with a higher $\phi$ (again to mantain valid the assumptions behind the formula) and higher rate of turn.
So, to conclude, assuming that you whish to perform a coordinate turn, whether the turn rate increases or decreases is a function of what you whish to keep constant when you change speed:

if you have a constraint on the bank angle, an increase of the velocity will decrease the turn rate and increase the turn radius
if you have a constraint on the radius, an increase of the velocity will increase both bank angle and turn rate

To complete the set of equations and see this in practice, you would need to flip each equation and apply it after the other. That means:

Case 1:

$$\dot\psi=\frac{g \cdot tan\phi}{v}   \;\;\;,\;\;\; r = \frac{v}{\dot\psi}  \;\;\;,\;\;\; \phi = const.$$

Case 2:

$$\dot\psi=\frac{v}{r} \;\;\; , \;\;\; \phi = atan\left( \frac{v \cdot \dot\psi}{g} \right) \;\;\; , \;\;\; r= const. $$
Note in case 2 how $\phi$ is computed through an $atan()$ function. This means that increasing $v$ will make $\phi$ approach $90^\circ$. The validity of the model used to derive this equations is no more guaranteed at that point.


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Are cabin dividers used to "hide" the flex of the airplane?
Recently onboard an aircraft, a fellow passenger told me that the cabin dividers (walls) inside an aircraft are there to limit your line of sight such that you will not notice the flex of the airplane.
I know that some walls are there because of the presence of a lavatory or are actually used to create a barrier between Economy class and Business class. However as can be seen in the photo below, the circled wall is doing none of the above.

Was my fellow passenger right?

I have heard that was such the case for particularly long aircraft (a340-600), from an Airbus employee... But they may have been misinformed themselves :)

Somehow I can't help but wonder if that passenger also believed that the aircraft were throwing out chem-trails...

Couldn't someone in an aisle seat poke their head around and see? Or am I misunderstanding?

Clearly, someone has never flown Southwest? :)

@CaptainMan, if you do that during taxi when all the curtains are open and you're sitting in the back of long aircraft such as the 777 you can clearly see the fuselage flexing as the plane rides over the bumps in the apron

Was my fellow passenger right?

No.
That photo is taken in a B777-300 (2 aisles, 4 seats in the centre and three at the sides, lavatories only behind the central rows, rows on the left side of the aircraft are one more than the central ones at that location):

As you can see the wall is just were an emergency exit is, and if you will look on the other side of the wall you will find a "jump seat", i.e. a foldable seat used by the crew, and the wall is there for it.
Also, walls help in dividing the aircraft in different classes.

Agreed, you really aren't going to see any flex, it's to separate the unwashed coach-dwellers in steerage from those willing to shell out triple the money for 2 inches more space.

@GdD 2" is a big deal if it's the difference between 1" shorter than your femur and 1" longer!

@GdD Or from those willing to shell out some points and $5 for a seat the folds out into a 6.5-foot-long bed. :) But, yes, you're right that those bulkheads are usually just cabin dividers unless there's a galley or lav or something there. Sometimes they're also for mounting FA jump seats by exit doors.

You won't be able to detect any flex in an airliner fuselage sighting down the interior without optical instrumentation of some kind, or a laser.  Where partition dividers are used without any obvious purpose, like separating classes or providing something to anchor something to, it's to break up "tunnel effect" of rows of heads in a tube out in front of you seemingly going to infinity, which some people can find disorienting when the big tube is moving, and can even aggravate motion sickness in someone prone to it.

If you're sitting in the back of a 777 and look forward during taxi when all the curtains are open you can clearly see the aircraft flexing if it goes over bumps in the apron

You could see the fuselage flex in the DC-8-71/73

It's an optical illusion.  There's flexing going on, but if it was flexing so much it was apparent to someone just sitting there looking down the tube, movement of inches in other words, I'd want out.

I've been in the rear of a 757 and looking down the aisle where the flex was all too apparent.

@JohnK good thing there are dividers, then. You're right about the reasons for the dividers, but you can certainly see flex if you look past them.


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Do airplanes dump fuel before landing?
Presumably planes aren't completely empty of fuel when the land, so they don't start refueling from zero, is that right? Is it true that they must dump excess fuel before they land? How much? Presumably not all, in case there's a problem with the landing and they need to abort?

@ymb1 not a duplicate, doesn't answer the question if they're empty on landing (they're not by the way)

Their can be reasons for a plane to offload fuel after landing (or before the next takeoff) but that would be more likely to apply to a small plane, where the weight of "full tanks of fuel" plus "the maximum number of passengers" exceeds the maximum takeoff weightof the plane. Of course you would try to plan ahead so this waste of money was avoidable. Except in very weird circumstances (e.g. the shortest commercial passenger flight lasts just 47 seconds, between two Scottish islands!) this would be irrelevant for a commercial airline

Don't you have any idea how expensive fuel is?

@kevin Likely the person asking the question does not know how expensive fuel is, and perhaps it's why they are asking the question. This site exists for people to ask questions. If people already knew everything the site would have no purpose. I don't know how expensive aviation fuel is either - perhaps it would be an interesting question to ask.

@DanieleProcida I meant it in an inoffensive, friendly tone (=

Yes, whenever I have excess fuel left at the end of a flight I fly over the parking area and see if any those jerkoffs flying Extra 300s or Pitts Specials are around and then I dump it on them.

I assume we're speaking of commercial air services such as airliners.
Generally, landing with less fuel is better than with more
It's better for an aircraft to land with less rather than more fuel. Fuel can make up a very large proportion of its total weight and it's inefficient and uneconomic to fly around unneeded fuel.
"Enough" fuel includes a safety margin
An aircraft will be despatched with more fuel than is required simply to get it to its destination: it needs to have enough to deal safely with unexpected headwinds, a long holding pattern before landing, a diversion due to an airport closure and so on.
A heavily-fuelled aircraft can be "overweight" for landing
Above a certain weight, an aircraft exceeds its correct limits for landing. This can make landing difficult and at worst could damage the airframe through over-stress.
If a landing is required before the aircraft has consumed enough fuel for a within-specifications landing (by some sort of emergency or an unexpected airport closure):

the pilot can burn off fuel in a holding pattern
fuel can be dumped if the model has that capability
the aircraft will land overweight if it lacks the capability or needs to land before fuel can be dumped

Aircraft may routinely land with extra fuel
For operational reasons an aircraft may land with more fuel on board than was needed for a particular flight - for example, it may be less expensive to carry the extra fuel than refuel at a particular stop.
In short
The general answer however:

Aircraft will be fuelled to land with the minimum possible unnecessary fuel.
If an aircraft has to burn off or jettison fuel before landing, that's not a routine operation, and it indicates that something has gone wrong.

You seem to be suggesting that excess fuel is routinely dumped by commercial airlines in non-emergency situations. I am fairly certain that is untrue.

It's most definitely not the case! What makes you think I'm suggesting that? If it's ambiguous it needs to be changed.

Read your fourth paragraph carefully. It suggests that if a plane is above weight, it will only land at that weight if there's a problem. But otherwise, if it needs to land at above weight, it will dump fuel if it has that capability. That is not true.

@DavidSchwartz I'm not sure what you think is not true. An aircraft that lands overweight does so only because of a problem. If there is a problem that requires a landing while overweight, fuel will be jettisoned if possible. However I will rewrite to clarify.

Your answer now explicitly states that an airliner that is overweight to land due to an airport closure would dump fuel in a non-urgent situation. (Well, technically it says fuel "can" be dumped, but of course it wouldn't be.) You've combined the emergency procedures with the routine ones in that list.

@DavidSchwartz You can't land at the destination airport because the runway has been closed due to bad weather. The two airports you can reach with your fuel will close their own runways (also for bad weather) in less time than it will take you to burn off the fuel you're carrying. So, you will dump it if you have the capability.

Right, but not because of the airport closure. Because of all the other factors you mentioned. You would never dump fuel because of an airport closure. You would not a case where not dumping fuel would create some real problem.

@DanieleProcida, if your choice of airport is limited by available fuel, you are way below MLW.

@DanieleProcida, if the destination airport is closed, you are going to the alternate and that is close to the destination, so you have/will burn all the fuel planned to go to destination, plus possibly some more depending on when you decided to divert. You don't have anything to dump either way.

@JanHudec All kinds of wholly unexpected things can happen - and have done. Airspace can be shut down across a nation. A war can break out. Freak weather conditions can erupt very fast. The circumstances might be unusual or even extremely rare, but that's not the same as saying that there are no conceivable conditions under which they might arise.

@DanieleProcida That's a silly argument. That's like saying it's reasonable to say you might need to cut of your arm because you're late for lunch (without qualification) because it's theoretically possible to imagine an incredibly rare chain of events that starts with you being late for lunch and ends with you needing to cut off your arm. Is is absolutely not procedure to dump fuel because of an airport closure, and your answer says it is.

@DavidSchwartz "Silly" or not, it's something that has happened. When airspace and airports closed across the USA on 11th September 2011, many flights were forced to dump fuel in order to land as quickly as possible. That's the nature of emergencies in aviation: they're rare, and they can involve extraordinary chains of events.

@DanieleProcida I said the argument was silly and explained why. I didn't say it hasn't happened, just that it cannot form the basis for the argument you made. People have died from papercuts, but if you put death on a list of things that result from papercuts, you're just making a silly argument.

@DavidSchwartz: If someone asked the question "Do people die from paper cuts", it would be totally reasonable to answer "Generally no, but under certain rare circumstances it has happened" - that's hardly a silly response :)

Right, and that's what's missing from your answer.

@DavidSchwartz: My answer?!

Here's the TLDR answer.

Presumably planes aren't completely empty of fuel when the land, so they don't start refueling from zero, is that right?

Planes aren't completely empty when they land: you can tell this because they land with the engines on. And, as you say, they need sufficient extra fuel in case they have to abort a landing, or the airport is congested and they need to circle, or the headwinds were stronger than expected or a myriad of other things.

Is it true that they must dump excess fuel before they land?

Planes only dump fuel in emergencies, and not all planes can dump fuel. Fuel is one of the airlines' biggest costs so they don't routinely throw it away. Fuel may have to be dumped because the maximum allowed take-off weight is usually much higher than the maximum allowed landing weight: if you've flown, you can tell that landing is harder on the plane than taking off. Fuel can be around half the weight of the plane at take-off. In case of an emergency early in the flight, one has to weigh up the pros and cons of staying in the air longer to dump fuel and land within or closer to the allowed weight, versus landing overweight straight away.

Typically the aircraft is fueled with enough for the flight plus extra for one or two diversions beyond the destination.  Only in emergencies or when it's necessary will they land with over-excess fuel.
Having less fuel in the tanks is less fuel to burn if there is risk of breakup on landing or when landing gears can't be lowered into position.  Landing on the planes belly could puncture the tanks so this helps that.
Not all jets have fuel jettison capability, not on the typical Boeing 737 or Airbus A320 series, they can only reduce fuel by burn, so they'll fly around for hours in a holding pattern near the airport until safe to land.
Fuel dumping is built into the large wide body jets like a Boeing 777 or 747 and the big Airbus models.  This is due to their long ranges and large amount of fuel required for the journey, these planes are designed with a maximum take-off that is greater than their maximum safe landing weight.
Fully fueled, once airborne they cannot land while overweight or risk over-stressing the structure and possibly overheating the brakes.
There have been a few instances of Pilots being forced to land anyway, such as possible fire.  In every case a full inspection will be mandatory before the plane can return to service.  This depends on the damages, sometimes all is needed is another set of tires and brakes, or if the landing causes cracks in the structure it could be too expensive for repairs so is scrapped.

There have been many explanations given but ultimately the answer to your question is "No, aircraft do not dump fuel prior to landing unless it is absolutely necessary."
During an emergency fuel may be dumped to reduce landing weight and reduce the  likelihood of fire. These facts have been established by many others above.
What hasn't been covered is Speed. An aircraft carrying many thousands of kilograms of fuel requires higher speeds to keep flying. With higher speed you need more runway space to bring the aircraft to a stop. Dumping fuel reduces weight and therefore speed.
So, fuel is dumped to reduce weight, speed, braking distance and to reduce the chance of fire. Aircraft can land overweight but it is far from ideal and requires extra distance on the ground. Normally if a flight is closer to its destination fuel dumping might not be required, however closer to departure point dumping is more likely in an extreme emergency. Factors such as runway length and nature of emergency will influence the decision made by the Pilot In Command.
An alternative to dumping fuel is dumping passengers, and keep the fuel, but that requires a lot of extra paperwork and probably affects the pilots career :)

Landing overweight also requires that the airplane be taken out of service and inspected, which is even more expensive than throwing away fuel. While cost should never be a factor in making safety decisions, it can be factored in if all other things are being equal. For example, if the plane needs to go back for some non-critical issue (e.g. airconditioning broken), then the pilot will probably choose to dump (or burn) fuel rather than perform an overweight landing. If, OTOH, the airplane is on fire, he will land overweight, and risk the brakes overheating and the airframe overstressing.

@JörgWMittag Thinking about it from that perspective... what are the resultant costs of cleaning up after a fuel dump? It feels like if you dump several tons of volatile petroleum into the air, it's got to go somewhere. While in practice this is probably an external cost (ie, one borne by a third party) and the airline ignores it, I wonder if it's considered anywhere..

@Andrew read this for info on what happens to dumped fuel.

@Andrew: You dump several tons of petroleum into 5.5 quadrillion tons of air. Noone's gonna notice.

This wiki entry might be useful. https://en.wikipedia.org/wiki/Center_of_gravity_of_an_aircraft#Fuel_dumping_and_overweight_operations

A commercial airliner only takes the fuel required for the flight plan, this is calculated and provided to the flight crew prior to departure. They then decide the right amount taking into account weather, potential delays etc... This is normally just enough for the leg to be flown i.e. fuel from departure to destination plus reserves and alternate fuel.
Commercial aircraft are required to land at destination with final reserve fuel, which dependant on the national authority is the minimum fuel required to fly for 30 (or 45) minutes at 1,500 feet above the alternate aerodrome. You can burn your alternate fuel if you're confident in landing at destination. If it looks like you're going to land with less than final reserve you are required to declare an emergency.
So to answer the question, no dumping fuel is not routine, you will always land with some, the amount depends on the type of aircraft type.


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In which cases the lift distribution is not elliptical? (i.e. e≠1)
I understood that Oswald coefficient doesn't modify the induced drag (i.e. =1) if the lift distribution is elliptical.
When is the lift distribution not elliptical? What are the physical or ideal causes?

When is the lift distribution not elliptical?

The distribution is non elliptical basically always, you have to struggle quite a lot to achieve an elliptical distribution.
As far as I know only the Spitfire managed to decently approximate the elliptical distribution, and even then, the unavoidable presence of the fuselage had its consequences.

What are the physical or ideal causes?

Ideal? I think you are confusing what is ideal here. The ideal case is the elliptical distribution, since it gives you the minimal induced drag for equivalent lift.
As basic theory goes, you can have an elliptical distribution with an elliptical wing (is a consequence of the so-called lifting-line theory).

but why normally the distribution is not elliptical? Is it for example caused by not perfect wing surface quality of finishing? Or interruptions?

@d.pensopositivo as I mentioned, the presence of the fuselage (and all the stuff attached to the wings) is one such reason. The shape of the wing is another (swept, non elliptical distribution of chord, etc.) I suggest you become a little familiar with the lifting-line theory, it explains a lot.


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Are tail strike landings preferable for an emergency landing on water?
In this video, would it have been better if the pilot had attempted a tail-strike landing instead of a normal flare?

Very closely related. FWIW, the currently accepted answer there shows the ditching checklist for a C152 and the same instructions are used for the 172 and 182 too: touchdown should be level, at low airspeed and with the gear retracted (if applicable). That might be different for other aircraft, though (the Cirrus would be an extreme example).

Rare successful ditching of a transport aircraft. Related: Effect of pitch angle on initial stage of a transport airplane ditching. Directly to the conclusion: 10 to 12° (for a transport aircraft).

Need answers quick, lake approaching fast.

While there probably is an "ideal" attitude to impact water, and it would be nice to crash-land with exactly the correct attitude... it's very much a secondary consideration.
By far the most important thing, when landing on water, is to land slowly. As such, your aim should be to land (/crash) with whatever attitude gives the lowest possible ground speed/descent rate at the point of impact. If that means a "normal" flare, do a normal flare. If that means a harsher flare with a tail strike, do that instead.
The point is that you're in an emergency situation, and your biggest priority is to get the speed right: you likely don't have the luxury of trying to fine-tune your angle of impact and flare. Additionally, you always have the risk of over-flaring and stalling into the water instead, which is a worse end result.
So yes, it may - with some airframes - be beneficial to have a tail strike, but you're far better off just keeping the aircraft under the best control possible and reducing your speed as far as possible

Another consideration for water landings, is that you don't want to have an impact that would damage the rear of the aircraft. If you end up making a hole or something somewhere near the rear, the plane will fill up with water much faster.

Everybody has brought up good points. I'll mark this as the answer because it has the most up-votes.

Having your tail hit the water first probably isn't the best idea.  Remember, impacting the water will slow your plane down very quickly, which will take away all the lift your wings are generating.  Thus, it would likely drop the front of the plane into the water, possibly at a very high speed.  It would be preferable to avoid such an impact.
The best practice would be to land as slowly as you can (like Jon Story said), while doing the best you can to keep the plane level with the water (though, as Jon stated, that would be a secondary consideration to keeping the speed low.)

But would the body of the plane be going faster when it hit the water than if it was the first part of the plane to contact the water?  Getting some deceleration from just the tail before the full drag of the whole body touching the water might help to spread the deceleration over a longer time, reducing peak g forces, even if that means some vertical g from the body slamming down.  OTOH, if the body slams down and gets more water contact than with a gradual entry, that spike in drag could be a worse spike in total g, esp. since it comes at the same time as vertical g.

A fixed gear aircraft like that in the video will almost certainly flip over no matter what technique is used. The main wheels are well below the aircraft's center of mass, are going to contact the water while the aircraft is still moving forward at a significant airspeed, and will create a very large drag force as soon as they do. It all adds up to an upset moment far larger than the tail can counteract, so the aircraft will at the very least upend, if not rotate all the way onto its back as in the video.
The picture can be more favorable for a retractable gear aircraft if the wheels are up at ditching. Even then, it's possible for aquatic drag forces to create a large enough pitching moment to cause the nose of the aircraft to "dig in".
Touching tail first will probably make little difference. For the aircraft to settle rather than slam onto the water, the wings have to be generating enough lift to support it, which means the aircraft still has to be at flying speed at the moment it contacts the water, which means huge drag for whatever is in contact with the water.

It's pretty dependent on the structural integrity of the airplane, and water-landings aren't an exact science to begin with.  If the tail of an aircraft can withstand the sudden deceleration of striking the water without breaking off, then a tail-first landing should be ok, if the AoA is still close to level.  This will ensure that the aircraft doesn't flip tail-over-nose when it does finally settle in the water (if, for example, the "landing" speed is too high).  Put the tail in the water at too high of an AoA though, and the sudden deceleration of the tail will cause the nose to slam into the water quickly.  Alternately, it can break the tail off the aircraft.  This would allow water to flood into the aircraft, causing it to quickly sink.  Definitely not optimum if you have passengers to evacuate.


text:
How to get a home base airport in the UAE?
How can you get a permanent home base airport in the United Arab Emirates, if your company is registered in different country?

I don't really understand your question. Are you asking how an airline based outside the UAE could use the UAE as its base/hub?

Yes, that's what I would like to know.


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Why did only Boeing choose to use 4-engines on the B-17?
The USAAC announced a competition in 1934 for a new multi-engined bomber with the requirement that it carry ~2000 lbs of bombs 2000+ miles at 200+ mph (with 250 mph preferred). The three entrants to the competition were famously the Douglas B-18, the Martin 186, and the Boeing Model 299, which would go on to become the B-17. The core difference in design taken by Boeing relative to the other two competitors came in the choice of the number of engines and thus the possible size of the aircraft that could be designed. Boeing decided to use 4 engines, allowing them to design a much larger aircraft that had higher range and bombload than the competing designs. Why did Douglas and Martin choose not to design 4-engined bombers for this competition?

According to Wikipedia "while the Boeing design was clearly superior, its four engines eliminated it from consideration and the crash of the prototype put its purchase on hold". Apparently Boeing built a prototype that was not in line with the requirements (it was twice as big as the other two!), basically betting that at a certain point during the war the Army would have needed it. Their bet was right.

Is your question "Why did Boeing choose to use 4-engines on the B-17?" or "Why did Douglas and Martin choose not to design 4-engined bombers for this competition?". They don't seem like the same question at all.

Both questions. I think they are intertwined. Clearly the Boeing and Douglas engineers made a different technical choice and I think the question is understanding why each group made the choice they did. So understanding both the thoughts of the Boeing engineers and Douglas engineers is valuable.

Martin actually did have a competing design, the twin boom XB-16 that went along with the Boeing XB-15 submitted for another USAAF requirement to travel 5000 miles.
Douglas, after their enormously successful DC-3, also had a 4 engine DC-4E airliner on the drawing board.
But Boeing was simply in the right place at the right time with proven experience that resulted in designs such as the 314 Clipper and not only the B-17 bomber, but also the 307 Stratoliner.
As it turned out, even though the Martin and Douglas designs were light years ahead of designs from the previous decade and as fast as contemporary fighters of the early 1930s, the decision to adopt the larger 4 engine Boeing aircraft as "heavy bombers" paid off in better defensive capability, larger payload, and longer range.
The two engine designs lived on as "medium bombers" better suited for shorter range tactical support missions.

@quietflyer try this one.


text:
Does a new FAA medical supersede and void an old medical?
If this seems like a rant it's not intended to be, but an actual issue I'm facing.
Scenario: I've been on disability for about a year and a half, and I'm ready to get my Medical back and go back to work.  I've followed everything that ALPA my union said to do, and what the FAA has sent me in the process. AMAS (ALPA Medical) told me to get a deferred medical after I sent all my medical documents to the FAA.
I go to my AME and get a 1st class medical and pass it, but it has to be deferred, and the FAA has to approve it. So my AME sends it off to the FAA after a period of time I get a letter from them saying I need to go do another medical, so I go do another medical.  But it's been less than 90 days, so my AME cannot print out a medical, so he contacts the FAA again, they say they are sending my medical to me.  Several weeks later I get a medical that shows 10/17/22 for the date (original date I did the medical). It shows it was printed out the day before I got my second medical exam and mailed on 11/19/22 (according to date on the bottom of my medical paperwork).
I decided to look at my PRIA information, and it shows 11/16/22 as my Medical date.  I know that's not the date my medical shows.
I call the FAA about my medical. After I spoke with someone I told my situation to, and she looked and didn't see an issue at first, but then she found the 2nd medical dated on 11/16/22 in the system.  She says contact my AME and see if he can print out the 2nd medical, and if he cannot print it have him call the FAA.  So I call my AME and his secretary says she can only find the original 10/17/22, they have not received anything else from the FAA and they don't want to deal with it, tell me to call the FAA. Grrrr...
Is my 10/17/22 medical legal to use even though I may have one with a date of 11/16/22?
I start indoc in a week for my job.  I don't want to get ramp/sim checked and have an issue... Does a new medical supersede the old one and make the old one void? They are both 1st class medicals.
I'm going to try calling the FAA again tomorrow, but I'm afraid they are going to say contact my AME again, and he's not going to be of any help.

I have no idea, the FAA's medical system is an enigma to me. You may get knowledgeable answers on this site (and I hope you do as I feel your pain), but your question's title uses the word opinion, and based questions are off topic so this could get closed. I suggest you reword it, and also edit it so it's a bit less of a rant, as TBH it's a little hard to follow.

I followed your advice, and rewrote it  somewhat..

I’m voting to close this question because this is asking for direct legal advice

May want to try the advice given in the answer to this question and see if you can get a copy of the new medical that way.

That works for me @Brad, it sounds like you got a workable answer and it's good you posted it as it may help others.

Not an answer, but I suggest calling or emailing your Regional Flight Surgeon for a copy of the new cert.

I'd also write your Congressman/woman, this is the kind of runaround that the federal agencies are not supposed to create.

After contacting the FAA today on this phone number: 405-954-4821 regarding my medical status. They concluded that my 10/17/22 medical is invalid because a new one has been issued on 11/16/22.
Once a medical has been issued, the old one is invalid.

Since (it sounds like) your new medical was issued by the FAA (rather than by an AME), was the FAA able to provide you with the replacement hard copy of it that you need?

Yes, they emailed me a copy of my medical.


text:
What is a good spin aircraft for someone that is heavy?
I've been trying to get a spin endorsement for my CFI, but I've been having a problem trying to find an airplane that I can do it in.
I'm 280 built like a linebacker.  I'm not that "fat" just heavy.  Losing weight for me isn't really a realistic option since I'm on a time crunch.
The closest thing I have found is an Xtreme Decathlon Citabria, but the CFI I go up with needs to weight 110lbs or less, and I'll probably have to stop for fuel in the middle of the flight.
I was told maybe a 172P model might work since it's utility class is 2000lbs, but I've not found one anywhere locally to verify this and see if they would be willing to let me spin the aircraft.
I'm in DFW, but I'd like to keep this question as generic as possible since others may want to know what other aircraft options there are.  But if you know of and airplane in the DFW area (or surrounding areas) please let me know.

This place has an Extra 300 which should have enough UL for you and an instructor and be fine to spin.

AFAIK, all C172s are approved for spins. The N-S models are, and I randomly checked an older H model POH and it is too. Always in the utility category, of course, and subject to what the operator, insurance, club rules etc. allow. Those things are probably a bigger issue than finding a C172, but you also have to find one that you can load and stay in the utility category, of course. Every aircraft is slightly different.

I second what @Pondlife said: certainly the C172 M and R models are also spin approved. Just looked up the data for the C172M that I flew most recently and it would be in the utility category with 20 gals of fuel (2.5 hrs), 280 in the left seat, and 130 in the right seat. I'm sure many similar aircraft are out there.

The "P" Model has a higher Utility class weight than the other models that I've looked at.  The "S and R" models I will be outside of the utility class in with most instructors.

@Brad did you ever solve this? I am in a similar situation (https://aviation.stackexchange.com/questions/31755/is-there-anything-extra-required-to-spin-a-cessna-172-in-the-utility-category) but I think I have found a place in Fullerton, California that can accommodate me.

@Canuk No, I lucked out and found a logbook that I thought was lost in a move which has my spin endorsement from 14 years ago. I was about to go up in a t-28 trojan to do my spins, but found my logbook.  You "might" fit in one of those, but I'm not sure at your height.

A Cherokee 140 should do it. Fill to just below the tabs and get an instructor that weigs 180 lbs.

Anyone know of a Cherokee 140 in the DFW area that I can do the spins in?

I'm a large individual myself, like you describe: tall but proportional, and was in a similar situation. In 2017, I found a place in Fullerton, CA that was able to accommodate me.
We used a Waco YMF-5C. With no canopy, my height wasn't a problem and we were well within CG limits and weight capacity (the front seat is designed to hold two "average" people).

Awesome, I bet that was fun!

Check out Four Winds aviation in McKinney, TX.  There deal in aerobatic training and operate Decathalons, S-2Bs and an Extra 300L.  Explain your situation to them.  I believe it may be possible to do so in the Extra 300 with a light instructor onboard as well.
Off topic, but I'm not sure if any of these places are going to have emergency parachutes designed for a guy your size; that may be a deal breaker as well.
I would really not seek out spin training in a CE-172s, Cherokees and other trainers certified to spin in the Utility category envelope.  These airplanes can be tricky to goad into a spin.  In addition most IFR-equipped trainers are going to have gyro driven AIs DGs and turn coordinators and spinning will precess them to the point of being unreliable.  Makes the FBO management cranky and few friends for you.

Parachutes are not required for spin training; see §91.307(d). Additionally, C172s are routinely used for satisfying the spin training required of CFI applicants.

I tried Four Winds, we were out of weight and balance in their aircraft.


text:
SPL/TMG -LAPL-A to PPL
If you follow the educational path from Sailplane Pilot License / Touring motorglider (SPL/TMG) to Light Aircraft Pilot Licence (LAPL-A/SEP).
What is the requirement to progress from LAPL-A to a Private Pilot License (PPL)?
Can you fly TMG to collect the hours on the way to PPL?  Navigation flight?  Solo flight?
Can you use an SPL/TMG flight instructor in that process?


text:
What is the standard procedure in case of inconsistent sensor readings?
After reading the answers I now know there are three independent sensors. I will leave the question as-is, to not take the answers out of context:
I do remember reading that airliners have two independent sensors and channels to deliver readings like airspeed and altitude to the cockpit (pitot-static system).
  If this is not the case my question will not make sense.
If the two systems show conflicting information, what is the standard procedure? If one of them is 'overspeed' or close to stall speed should the pilots assume this is the one to focus on? Or do the pilots reason based on each situation independently and all the other factors at play?

The procedure used would depend on which information is conflicting/unreliable (and of course the aircraft type).
With one or more unreliable airspeed indications (which is one of the more critical ones), the initial action is NOT to start troubleshooting/figuring out which indicator is "the correct one", but to ensure safe speed/flight path by other means. The initial actions on Boeing aircraft is to disconnect automatics (auto throttle, autopilot, flight director) and control the aircraft given memorized combinations of pitch and thrust. With the aircraft under control, and when directed by the checklist, you start analyzing the situation, to see if you can rectify/isolate the faulty source. If a reliable source can not be determined, the aircraft continues to be flown by pitch/thrust settings given in the manual (based on altitude, if known, weight, flaps/gear, desired vertical profile etc).
In the case of unreliable altitude, in case you can't determine a reliable source, you can typically use radio altitude below 2'500 ft. A big caveat is that if the transponder is set to use an unreliable static pressure source, the altitude that ATC sees on secondary radar will also be unreliable. An example of this was seen in the Aeroperú 603 accident, where the aircraft took off, with the static ports taped over, and ATC was asked to assist with altitude and speed information: CVR transcript - Wikipedia
Erroneous airspeed/altitude indications often imply each other, as an unreliable static pressure source will affect both.

Avionics computers are generally (if not always) triple redundant to avoid the very situation you bring up. Form a pure logic standpoint you cant know which reading is correct if you only have 2 readings in a blind situation. However if you have 3 readings, 2 in agreement and 1 that differs you can statistically assume that the 2 agreed readings are correct. There is a nice summary here on Wikipedia. This Question on why there are multiple autopilots also addresses it nicely.

Avionics sensors are, indeed, usually triple-redundant. It does not apply to avionics computers, where the redundancy (for the critical systems like FBW) relies on dissimilar systems instead.

Interesting, my understanding of FWB was that it was also triple redundant but I learn something new every day.

I don't know about Boeing, but in Airbus ELACs and FACs are only two and only SECs are three, but fault detection does not seem to use cross-checking between them anyway. Instead each unit is a pair of computers, one checking the other. See also http://aviation.stackexchange.com/a/15262/524.

There are at least three systems. You compare indicators with the standby system and know which one of the main systems failed. Sometimes all systems can fail due to icing or bird strikes. In this case there is an unreliable air speed procedure or checklist. Basically aircraft is flown by pitch and power settings.


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What is the parasite drag for Airbus A320?
What is the parasite drag or CD,0 for the Airbus A320?
How do we calculate CD? Is it correct to use CD = CD,0 + ( CL2)/$\pi$AR

A good aircraft design has a $c_{D0}$ of 0.012, an average one 0.02, and bad ones exceed 0.03. If the gear is not retractable or the wing is held by bracing wires, the  $c_{D0}$ can even reach 0.05. Gliders have a $c_{D0}$ of below 0.005 at high speed. Calculation is hard: You need to bookkeep the contribution of every component.

For numerical usage (in some question) you can use the above formula, but for exact drag (and lift) calculation, the industry standard is to use Computer Solvers to compute this drag because of the following reasons:

The formula used above is correct but the value of Cd varies for every point on the wing, as things like wing twist, sweep back, wing tip sharklets contribute to a different Cd throughout the wing.
Other effects like drag due to fuselage etc can not be calculated by using a generalized equation for the whole plane, as usually local Cd for every point on the airplane surface are known.
Application of force on the surface of an airplane (Lift/Drag force) causes deformation in the geometry of the surface and this leads to recursive change in the value of Cd/Cl, which hence needs further set of calculation to again arrive at a value of Cd from the Solver.

For approximate usage though an averaged out Cd, Cd0 and AR if known, then the above formula can be applied to arrive at the results.


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What happens with RNAV procedures on the way from AIP publication to FMS database?
I'm particularly interested in Approach procedures, but I guess it applies for RNAV procedures in general.
On one side, the national Air Navigation Service Provider (ANSP) is responsible for the design of the procedure. The procedure charts are usually available as PDF files through AIP website (e.g. the terminal procedures available at FAA).
On the other side, the RNAV procedure is coded in binary format inside aircraft's FMS. The airborne databases that can be directly loaded to the FMS are provided by external companies (Jeppesen, Lufthansa, Navigraph).
What happens between those two points is kind of puzzling for me.
I know of ARINC-424 standard for aircraft navigation data that is used for "preparation and transmission of data". Then there is AIRAC cycle which as I understand provides fixed dates for any changes to become effective.
The questions are:

Who takes responsibility that the database being sold to airline or any user reflects the original procedure published by ANSP?
How does the coding process look like. Is it based on PDF charts or there is another exchange format available (e.g. AIXM)?

Welcome to Aviation.SE. You might want to split this post up into several to only ask one question at a time.

Welcome rgolcz! Those are nice questions, and I have some reference material for that somewhere, so I'll brew up an answer later. I concur with usernumber though, it may be better to split it up into three questions. I suggest to keep question 1 & 2 together. Once those are answered you can fire off questions 3 & 4 with reference to the first questions.

An old document: Legal and Institutional Issues. Court cases on page 10.

Thanks. I've followed your suggestions (@usernumber, @DeltaLima) to split the question.

@mins This example is great. Would you mind to post it as answer under the new question: http://aviation.stackexchange.com/questions/19558/invalid-fms-data-real-life-cases. I've split the question.

The navigation database is technically a component of the GPS or FMS navigation system.  As such the manufacturer of the GPS or FMS is responsible for ensuring the database works with the equipment.

The database itself is usually prepared by a database provider such as Jeppesen. They have to work with the manufacturer to format and structure the database to work with the GPS or FMS.  After Jeppesen builds a database for a given cycle the GPS/FMS manufacturer will test the database before it's released.
Depending on their business agreement, the database subscription may be purchased from the manufacturer or direct from Jeppesen.
Jeppesen obtains the data from the ANSP and must process the data in accordance with RTCA DO-200B, Standards for Processing Aeronautical Data.  (Available for purchase from RTCA Inc.)

In the case of the FAA, the data is available in numerous formats, most commonly in ARINC 424 format.

There's a great deal of info available on the FAA Aeronautical Information Services website.


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Are the total hours of an aircraft based on flight hours or operational hours?
Are the Total Hours and Total Cycles of an aircraft based on the Flight hours or Operational hours of an aircraft?

Please mark the most useful answer as accepted answer.

Cycle
One takeoff and one landing makes up one cycle. Counting cycles is important to keep the number of times the cabin was pressurized (with the assumption that the airplane flies at high altitude). It is also significant for engine maintenance. A cycle and flight/operation time are not related.
Hours
This is the time when an airplane is in operation (more on this below).
Flight Time
Generally speaking, it is the time when an airplane is flying. It is the duration from when landing gears leave the ground to when they touch the ground again. Pilots are not paid by this. In my opinion, it is mostly used by flight trackers to inform people if an airplane has landed or not.
Operation Time
For GA airplanes, when the airplanes is started, Hobbs meter starts and it stops when the engine is turned off. Most commonly, this is how rental GA airplanes' rent is calculated.
For commercial airplanes, pilots pay clock starts when parking brake is released and ends when the parking brake is set.
Hence, total hours is more closely related to operation time.

If you are talking about total time and total cycles in reference of retiring an airplane, that is a different discussion. Each part of an airplane has a certain life. Though most of the time it can be predicted, but sometimes a certain component fails earlier than the expected life and therefore needs to be replaced. Airplane manufactures do specify a design life limit, but that is normally changed because of regular maintenance.

For pilot's paying time, please see this chat snippet.

I'm not sure about the total hours but cycles is based on take offs and landings. As per this article

the cycle count (takeoff and landing is considered an aircraft "cycle")

They also go on to say

or the number of hours flown since the last check

so I'm guessing it's flight hours. For what it's worth in small GA planes this is generally measured with a Hobbs meter which clocks hours based on the engine running. That does not mean you have left the ground. So any hour based service on a GA plane is going to be done on that clock not a flight time clock (which none of the planes I fly even track).